1. Field of the Invention
The present invention relates to a lighting and/or signalling device, in particular intended to be fitted to a motor vehicle, comprising at least one optical guide capable of diffusing light over at least a portion of its length. The invention also relates to a vehicle comprising a lighting or signalling device of this type.
2. Description of the Related Art
In the field of motor vehicle lighting and signalling, the use of optical guides is becoming increasingly common. An optical guide is, highly schematically, an elongate element made of transparent material, generally of cylindrical or similar cross section. In proximity to one of the ends of the guide, referred to as the input face of the guide, is arranged one (or more) light sources, for example a small, light-emitting diode-type light source: the light rays emitted by this source spread by total reflection over the length of the guide toward its opposing end, referred to as the terminal face of the guide. A portion of the light rays spreading into the guide issues through the face known as the front face of the guide owing to the presence of reflective elements arranged on the face known as the rear face of the guide, remote from the preceding face. These reflective elements consist, for example, of prisms. The guide thus emits light over its entire length. It has the advantage of being able to assume very varied geometric shapes, of being rectilinear or curved, and of conveying a lighting surface even into inaccessible zones of the headlamp or light of the vehicle. It thus makes an important contribution to the style of the headlamp or light.
These guides have to meet numerous requirements:
They have to be supply light into zones of the vehicle light or headlamp that may be inaccessible, and this in some cases necessitates the design of systems for conveying light to the input of the guide—the light source, for its part, being offset and remote from the guide.
These guides often assume complex shapes, with bends for example, and this often leads to undesirable leakages of light in the region of these bends, and therefore to reduced lighting power of the guide downstream of the bend (the terms “upstream” and “downstream” being understood as a function of the general direction in which the light spreads into the guide).
The zone for coupling between the light emitted by the light source (directly or via a light conveying element such as a fiber optic) and the guide is also awkward to design, as misdirected light has to be prevented from escaping at an untimely moment out of the guide or from failing completely to return therein. This problem is encountered, in particular, in guides having a closed or almost closed contour, in which there is observed, when the guide is switched on, a high-intensity light point emitted by the coupling zone (light point also referred to as a hot spot), thus reducing the light output of the guide over the entire length thereof and providing the guide with an unattractive, non-uniform appearance.
There is, for example, known from the application for utility model FR 2 828 267 an annular-type light guide: the light flux passing into the guide is divided in two and issues in opposing directions into the annular guide by way of an injection element conveying the light perpendicularly to the plane of the ring. This injection element is associated with an injection surface comprising two surfaces diverting the light, so that it is reflected toward the guide in order to spread at this location. This light injection system is capable of improvement, as it still generates leakages of light: the guide still has in the region of this injection surface a hot spot which is detrimental to the appearance of the guide.
There is, therefore, a need to provide a system and method that overcomes one or more problems in the prior art.